The invention relates to a multistage crude gas scrubbing system having a high deposition level of dust in an entrained flow gasifying unit for the reaction of ash-containing fuels with a gasifying agent containing free oxygen to give a crude gas, while obtaining a high hydrogen content.
The invention further relates to process steps in an apparatus for treatment of circulation water in the cleaning of crude gases from an entrained flow gasifying plant, in which fuel dusts are reacted with oxygen and moderators such as steam or carbon dioxide at temperatures between 1200-1900° C. and pressures up to 10 MPa to give a crude gas rich in CO and H2.
Fuel dusts are understood to mean finely ground coals of different carbonization level, dusts formed from biomasses, products of thermal pre-treatment, such as cokes, torrefaction products and fractions having high calorific values from communal and commercial residual and waste materials. The fuel dusts can be supplied to the gasification as a gas/solid or liquid/solid suspension.
The gasification reactors can be provided with a cooling screen or with a refractory lining, as shown by the patents DE 4446803 and EP 0677567. In various systems introduced in industry, crude gas and the molten slag can be discharged separately or together from the reaction space of the gasification apparatus, as described in DE 19718131.
Entrained flow gasification, because of the fuel particles ground to a dust and short reaction times in the gasification space, cause an elevated dust content in the crude gas. Depending on the reactivity of the fuel, this entrained dust consists of soot, unconverted fuel particles and fine particles of slag and ash. The size varies between coarse particles having diameters greater than 0.5 mm and fine particles having a diameter down to 0.1 μm. The separability of the particles from the crude gas depends on this diameter, but also on the composition thereof. In principle, a distinction can be made between soot and ash or slag particles, soot particles generally being smaller and more difficult to separate from the crude gas. Slag particles have a higher density and hence better separability but, in contrast, have a higher hardness and hence erosive action. This leads to increased wear in the separators and crude gas-conducting lines, and can cause safety-relevant leaks and lifetime restrictions.
For the removal of the dusts resulting from the fuels, various scrubbing systems are being used conventionally, as described in patent document DE 10 2005 041 930 and in “Die Veredlung von Kohle” [The Addition of Value to Coal], DGMK, Hamburg, December 2008, Schingnitz, chapter on “GSP-Verfahren” [GSP Processes]. According to this, the crude gasification gas leaves the gasification space together with the slag formed from the fuel ash at temperatures of 1200-1900° C. and is cooled in a downstream quench space by injection of excess water and freed of the slag and, to a small extent, of entrained dust, it being possible for the quench space to be configured as a cavity quench or provided with a crude gas-conducting central tube. A cavity quench system is disclosed, for example, in DE 10 2007 042543, in which the crude gas that leaves the gasification space is sprayed with water and drawn off in the lower section beneath a roof construction. DE 10 2006 031816 exhibits a clear quench space entirely without internals, with injection of quench water at one or more levels in such an amount that the crude gas is cooled and saturated with steam, and the excess quench water is drawn off in the lower section alone or together with deposited slag. Variants with a central tube are disclosed by the patents DE 199 52 754, in which the central tube takes the form of a Venturi tube, DD 145 860, in which the crude gas at the end of the central tube is subjected to additional scrubbing in the form of an airlift pump, and DD 265 051, where elements for distribution of the crude gas flowing out at the end of the central tube are supposed to ensure uniform flow outward.
The solution according to patent DE 10 2007 042 543 has the disadvantage that the cavity, as a result of pipelines of relatively high diameter for the removal of crude gas and the roof construction, offers deposition surfaces for entrained slags and dusts, which, as experience has shown, leads to blockages. DE 10 2006 031816 requires homogeneous flow of the hot crude gas out of the gasification space, because there could otherwise be the risk of thermal overloading of the pressure-bearing vessel walls. The arrangement of a Venturi tube according to DE 199 52 754 can lead to unwanted variations in pressure in the gasification space, and these can barely be compensated for by means of control technology because of their short duration of action. Internals in the quench space and scrub space, as in the patents DD 256 051 and DD 224 045, can lead, as a result of the puzzolanic properties particularly of the fine dust components in the case of particular coal and ash types, to accumulating deposits having the strength of cement, which likewise lead to blockages and to an increase in pressure drop.
The problem addressed by the invention is that of providing a quenching and scrubbing system for an entrained flow gasification reactor for cooling of the hot gasification gas and the entrained liquid slag, wherein both cooling of the hot crude gas down to the water vapor saturation temperature determined by the process pressure and simultaneous deposition of slag and dust are to be achieved. In addition, the conversion and reaction between carbon monoxide and water vapor which thus proceeds is to lead to a relatively high hydrogen content in the crude gas.